A. Perhaps. There’s research that links drinking certain types of soda with weaker bones—but carbonation doesn’t seem to be the problem.

Nutrition experts once believed caffeine could be the culprit. In a 2001 study out of Creighton University in Omaha, Nebraska, people lost measurable amounts of calcium after drinking caffeinated sodas. Drinking decaffeinated sodas didn’t appear to have the same effect. As it turned out, though, people tended to make up for the losses by excreting less calcium later in the day. The researchers concluded that if sodas harm bones it’s probably because people drink them in place of milk.

But another study, reported in 2006 by researchers at Tufts University in Boston, suggests that colas, specifically, might be problematic. Among the 1,413 women whose dietary records and bone-density scans they reviewed, those who drank a diet or regular cola at least three times a week over five years had significantly lower bone densities than those who sipped cola once a month or less. No such effect occurred with other carbonated drinks, even after researchers factored in intake of calcium from foods.

The likely cause? Phosphoric acid, which is unique to colas, says Katherine Tucker, Ph.D., lead author of the study. When the body breaks down this compound, the acidity (or concentration of free hydrogen ions) of the blood increases. To neutralize acidity, hydrogen ions bind with minerals, including calcium and magnesium. If they’re not available in the blood, says Tucker, “the body draws calcium from bones.” The occasional cola drinker probably needn’t worry. “The real risk is for those who drink cola every day,” says Tucker.

Bottom line: There are plenty of good reasons to quit a regular soda habit; carbonation isn’t one of them. In fact, sparkling mineral waters sometimes contain a little calcium and magnesium, says Tucker, “so they might even benefit bones.”